In recent years, liquid crystal display devices are used in various applications. Liquid crystal display devices are used for, for example, display of instruments on a dashboard of an automobile. In general, devices for automobile use are required to operate in a wider temperature range than that of devices used indoors. However, the response speed of liquid crystal is slow at low temperatures. Hence, liquid crystal display devices for automobile use have a problem of a slow response speed at low temperatures. The slow response speed not only gives a poor appearance, but may also cause trouble in safety.
Meanwhile, from the viewpoint of an increase in contrast and design, there is a strong demand for normally black mode. In a normally black mode liquid crystal display device, a low voltage is applied when a low gradation is displayed, and a high voltage is applied when a high gradation is displayed. In a VA (Vertical Alignment)-type liquid crystal display device having normally black characteristics, the response speed is slow when a low gradation is displayed. Therefore, when a VA-type liquid crystal display device is used for automobile use, the response speed when a low gradation is displayed at low temperatures is particularly problematic.
In connection with the invention of the present application, the following documents are known. Patent Document 1 describes that each pixel of a liquid crystal display device is provided with two subpixels, and a drive signal that rises in a low-gradation area is applied to one of the subpixels and a drive signal that rises in a high-gradation area is applied to the other subpixel, by which the gradation characteristics for an intermediate gradation area is improved. Patent Document 2 describes that in a color liquid crystal display device, the gradation values of subpixels are modified to reduce the number of subpixels that display halftones, by which viewing angle characteristics are improved. Patent Document 3 describes that in a liquid crystal display device, a drive voltage is applied to liquid crystals of pixels only for a predetermined period of time during one frame period, and the application time of the drive voltage is changed according to the magnitude of a data voltage, by which viewing angle characteristics are improved. Patent Document 4 describes that each pixel of a liquid crystal display device is provided with two subpixels, and the difference ΔV between effective voltages applied to the two subpixels for a gradation gk in a given range is set to satisfy ΔV(gk)>0 and ΔV(gk)≧ΔV(gk+1), by which the viewing angle dependence of γ characteristics is improved.